In a substrate processing apparatus including an accommodation chamber for accommodating a substrate, e.g., a semiconductor wafer, therein and a mounting table arranged inside the accommodation chamber to mount the wafer thereon, when the wafer is subjected to a plasma processing, a plasma is generated in the accommodation chamber and the plasma (electrons and positive ions) is attracted to the wafer mounted the mounting table by supplying a bias power to the mounting table.
Typically, a semiconductor device is manufactured from a wafer. If particles in the accommodation chamber are attached to the wafer during the plasma processing, a defect is caused in the semiconductor device. Accordingly, several techniques have been developed to remove such particles from the accommodation chamber before the plasma processing.
However, for example, a part of a component in the accommodation chamber may be worn out to generate particles during the plasma processing. Such particles are positively or negatively charged. If the plasma disappears after the plasma processing, a negative bias potential is generated on the wafer. Accordingly, after the plasma processing, positively charged particles may attracted and attached to the wafer by an electrostatic force.
For that reason, a technique has been developed to prevent a self bias potential from being generated on the wafer and positively charged particles from being attracted to the wafer by performing a plurality of plasma processings without any intervals between the plasma processings to continually generate plasmas when the wafer is subjected to the plasma processings (see, e.g., Japanese Patent Application Publication No. 2003-068708 and corresponding U.S. Patent Application Publication No. 2003/3758 A1).
As shown in FIG. 4A, during the plasma processing, a negatively charged particle is mainly affected by a gravity FG, a force FE generated from an electric field caused by a bias power supplied to the mounting table, and a viscous force FN of a gas flowing inside the accommodation chamber.
In a mounting table 100 to which a bias power is supplied from a bias power supply 101, a negative bias potential is generated. Accordingly, when the mounting table 100 is a lower electrode, the gravity FG and the force FE have opposite directions. If a particle P moves distantly from the mounting table 100 by a predetermined value, the gravity FG has the same magnitude as that of the force FE. Therefore, the particle P stays there and floats around an interface of a sheath 102 over a wafer W by the viscous force FN as shown in a dotted line of FIG. 4B.
However, after the plasma processing, if supplying the bias power from the bias power supply 101 is stopped, no force FE acts on the particle P. As a result, as shown in FIG. 4C, the particle P falls downwardly by the gravity FG to be attached to the wafer W.